Vireo Vir"e*o, n. [L., a species of bird.] (Zo["o]l.)
Any one of numerous species of Americansinging birds
belonging to {Vireo} and allied genera of the family
{Vireonid[ae]}. In many of the species the back is greenish,
or olive-colored. Called also {greenlet}.
[1913 Webster]

Note: In the Eastern United States the most common species
are the white-eyed vireo ({Vireo Noveboracensis}), the
red-eyed vireo ({Vireo olivaceus}), the blue-headed, or
solitary, vireo ({Vireo solitarius}), the warbling
vireo ({Vireo gilvus}), and the yellow-throated vireo
({Vireo flavifrons}). All these are noted for the
sweetness of their songs.
[1913 Webster]

vireo — (n.) 1834, from L. vireo, a word Pliny uses for some kind of bird, perhaps the greenfinch, from virere be green (see VERDURE (Cf. verdure)). Applied in modern times to an Amer. bird … Etymology dictionary